1. Field of the Invention
The present invention relates generally to the field of wireless communication, and particularly to the design of an antenna on a wireless device.
2. Description of Related Art
In portable wireless communications, the radio transceiver needs to work adjacent to a radio absorber, like the human body, or like a laptop computer that has radio absorbing components. Because of this absorption, energy is wasted, and the radio transceiver is often less than 50% efficient. This means that the talk time of a cellphone can be increased by making the antenna more efficient. Alternately, the battery can be reduced in size, saving cost and weight. Similarly in receive mode, the antenna will receive more radio energy, and there will be fewer dropped calls in poor coverage areas, and in buildings. In addition, there has been speculation for some time that the radio energy absorbed in the body might be producing health effects. Accordingly, there is a need to provide effective shielding between the antenna and the absorber.
The invention discloses a metallic border that has a width comparable to the thickness of a spiral sheet antenna which provides an effective shield, as measured by the front-to-back radiation ratio. The spiral sheet antenna structure can be readily shielded from an absorber on one side by providing a metallic border, asymmetrically on one face of the spiral sheet antenna. For example a front-to-back ratio of 5 dB can be achieved by an asymmetric shield structure. The form of asymmetric structure is mathematically and geometrically specified by a geometrical procedure. Significantly, two holes or openings are asymmetrically placed so that they tend to face in the same direction, and away from the absorber. In one embodiment, both openings are facing in the same direction.
Advantageously, the present invention provides a shield to block radio energy from being absorbed in a body, which potentially could be harmful to a person""s health. The present invention also designs an antenna structure in which radio energy tends to flow in the direction away from a person.
Other structures and methods are disclosed in the detailed description below. This summary does not purport to define the invention. The invention is defined by the claims.